An input shaft receives driving torque from the vehicle driveline. For vehicles having forward and rear tandem driven axles, the input shaft then typically transfers driving torque to an inter-axle differential by being drivingly engaged therewith. The inter-axle differential then transfers driving torque to a forward differential and to a rear differential via an output shaft. Both the input shaft and output shaft are preferably rotatably supported by bearings.
Bearings, usually as part of a set of bearings, are preferably supported by another structure. Traditionally, for bearing sets supporting an output shaft, an output tube is utilized to provide support for the bearings. When an output tube is utilized, the bearings are generally disposed within the output tube.
Bearings require lubrication to prevent excessive wear and heat buildup from rapidly occurring. In order to properly lubricate the bearings, the lubricant must pass from one side or face of the bearing to the other. Thus, for bearings contained within an output tube, lubricant must be able to pass through the output tube and it must be allowed to continuously pass from one side of the bearing set to the other.
FIG. 1 shows an output tube known in the art. Traditionally, output tubes are formed in a forging process. A forging process produces an output tube 10 with only one channel 12 for allowing lubricant outside the output tube 10 to lubricate the bearings inside. This configuration prevents the bearings from being properly lubricated. For example, with a single channel 12, lubricant can initially pass from one side of a bearing set to the other. However, with nowhere to go, the initial lubricant blocks additionally lubricant from passing across the bearing set. Furthermore, the lubricant that can not pass then prevents the initial lubricant from returning across the bearing face. Thus a single channel output tube allows lubricant to flow in, but prevents it from escaping and prevents the bearings from being properly lubricated.
Those skilled in the art sought to solve this problem by removing a portion of the output tube 10 to create a second channel 14 to allow lubricant to flow into and out of the tube 10. The second channel 14 was traditionally made by a drilling process after formation of the output tube 10. The second channel 14 thus typically had an elliptical, conical, or circular shape. FIG. 2 depicts an output tube known in the art and produced using a forging and a drilling process. To ensure that the all of the bearing sets in the output tube 10 were properly lubricated, the second channel 14 is typically drilled outboard of outboard-most bearing set.
Creating a second channel allows lubricant to flow through the output tube and pass from one side of all the bearings within the tube to the other. However, a two step process is costly and inefficient. Therefore an object of the present invention is to provide an output tube that allows the bearings contained within it to be properly lubricated and that can be made in a one step process.